Glutamate receptors are the primary mediators of excitatory synaptic transmission in the central nervous system. Kainate receptors (KARs), a member of the ionotropic glutamate receptor family, have roles in brain physiology and pathology that are poorly characterized. Natural source compounds have been useful tools for identification and characterization of these receptors and their role in many processes. In particular, dysiherbaine (DH) has been isolated from the Micronesian sponge Dysidea herbacea and has been found to be a potent kainate receptor agonist and subsequently, a powerful convulsant (Sakai et al., J. AM. CHEM. SOC. 1997; 119:4112-16; and Sakai et al., JPET 2001; 296:650-8)
Dysiherbaine is a structurally unique KAR ligand, with a glutamate backbone connected to a rigid ring structure containing a methylamine substituent at the C8 ring position and a hydroxyl group at the C9 ring position (Sasaki et al., Tetra. Lett. 1999; 40:3195-8). This unique chemical structure, along with the distinct pharmacological profile of DH, suggests it could be useful as a template for the generation of molecules with unique pharmacological profiles that target KARs. Toward that end, neodysiherbaine (neoDH) and MSVIII-19, a natural and synthetic analog, respectively, were characterized (Sanders et al., 2005; JPET; 314:1068-78). The structure of these analogs differs slightly from the parent compound DH; neoDH has a hydroxyl group replacing the C8 methylamine of DH and MSVIII-19 lacks both the C8 and C9 functional groups. However, these slight structural variations distinctly after the pharmacological profiles of these analogs.
Here, we further study the role that critical substituents, and the spatial orientation of these substituents, have on pharmacological activity for dysiherbaine and its analogs and derivatives. A second generation of DH analogs was synthesized based upon information obtained from the characterization of neoDH and MSVIII-19. These epimer analogs altar the orientation of substituents at several critical positions of the molecule and exhibit selective antagonist properties for the glutamate receptors GluR5 and GluR6 relative to other glutamate receptors.